The polyvinylidene fluoride (PVDF) piezoelectric thin film is a kind of piezoelectric polymer material. It has unique piezoelectric effect, and is widely used in vibration measurement and other fields.There are few reports on the output characteristics of piezoelectric thin films under applied stress. In this paper, the sensing mechanism and the equivalent circuit model of PVDF piezoelectric film are analyzed theoretically. And then the numerical model of piezoelectric film is simulated by COMSOL software. Finally, the dynamic responses of PVDF piezoelectric films with different excitation frequency, vibration amplitude and external stress are studied experimentally. The results show that the output signal amplitude of piezoelectric film has a linear relationship with the amplitude of the film, but not directly related to the external stress of the film.